Exposure apparatus and method, and device fabricating method using the same

ABSTRACT

An exposure apparatus includes a projection optical system for exposing and transferring a pattern on a mask onto an object, an illumination optical system for forming a secondary light source surface approximately conjugate with a pupil in the projection optical system, and for illuminating the mask, and a mechanism for making non-uniform at least one of a transmittance distribution from the secondary light source to the object and a light intensity distribution on the secondary light source surface.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to exposure apparatuses and devicefabrication methods using the same. The present invention isparticularly suitable for an exposure apparatus used formicro-lithography to form a fine pattern for semiconductors, liquidcrystal devices (“LCDs”), magnetic materials, etc.

[0002] The device fabrication using the lithography technique hasemployed a projection exposure apparatus that uses a projection opticalsystem to project a circuit pattern formed on a mask or reticle (theseterms are used interchangeably in this application) onto a wafer,thereby transferring the circuit pattern.

[0003] In general, the projection exposure apparatus includes anillumination optical system for illuminating the mask using lightemitted from a light source, and the projection optical system, locatedbetween the mask and an object to be exposed. The illumination opticalsystem typically introduces light from the light source to an opticalintegrator, such as a fly-eye lens, to obtain a uniform illuminationarea, and uses an optical-integrator exit surface as a secondary lightsource surface to Koehler-illuminate a mask surface via a condenserlens.

[0004] A most effective light source should be formed according toreticle patterns for high quality exposure. The effective light sourcemeans an angular distribution of the exposure light incident onto awafer surface. For example, this effective light source distribution isimplemented by adjusting to a desired shape a light intensitydistribution near the fly-eye-lens exit surface i.e., a secondary lightsource surface.

[0005]FIG. 9 shows a relationship among a secondary light sourcedistribution, a pupil transmittance distribution, and an effective lightsource distribution in a conventional exposure apparatus. Although thesecondary light source distribution may form various shapes including acircular shape and an annular shape according to reticle patterns, itindicates an illumination condition with coherence factor σ=0.8. As inthe illustrated secondary light source distribution, the conventionallight intensity distribution has been adjusted to be uniform or flat.Since the pupil transmittance distribution is approximately uniform, theeffective light source distribution becomes uniform on the wafersurface, providing σ=0.8 uniformly without any difference of effectivelight source distribution between an on-axis and an off-axis.

[0006] The resolution R of the projection exposure apparatus is given bythe following equation where λ is a wavelength of the light source, NAis the numerical aperture, and k₁ is a constant determined by adevelopment process and others:

R=k ₁(λ/NA)   (1)

[0007] The recent demands for highly integrated devices haveincreasingly required fine patterns to be transferred or higherresolution. From the above equation, a higher numerical aperture NA andreduced wavelength λ would be effective to obtain the higher resolution.

[0008] Thus, an exposure light source used for the exposure apparatushas shifted to a shorter wavelength from i-line (with a wavelength of365 nm) to KrF excimer laser (with a wavelength of 248 nm), ArF excimerlaser (with a wavelength of 193 nm), and even F₂ laser (with awavelength of 157 nm). NA has shifted larger from 0.7 to 0.75.

[0009] However, such a short wavelength as 200 nm or less and NA of 0.70or higher (i.e., high NA) have created a problem in that the secondarylight source distribution and the effective light source distribution donot accord with each other, and the effective light source distributiondoes not become uniform even when the secondary light sourcedistribution is made uniform, lowering the exposure performance.

[0010] In other words, the higher NA results in a larger light incidentangle onto each optical element, making it difficult to maintainconstant an angular characteristic of the transmittance (andreflectance) in a required incident angle area. More specifically, thetransmittance near the optical axis appears to be low because a lighttransmitting element, such as a lens, is thick at its center part andthin at its peripheral in view of the glass material's transmittance,but the transmittance at the peripheral actually becomes lower because acoating or reflection prevention film affects the transmittance moregreatly. This is because the transmittance decreases more remarkably asa refraction angle of light incident onto the optical element becomeslarger due to the coating, and the light transmitting through theperipheral of the light transmitting element has larger refraction anglethan that transmitting through its center part. Although theconventional design technique has succeeded in maintaining within apermissible range, the transmittance reduction caused by the refractionangle at the peripheral, the refraction angle has become larger with thehigher NA and the transmittance reduction has been unable to bemaintained within the permissible range. In addition, the shorterwavelength limits usable materials for a reflection prevention filmapplied onto the transmission member, and restricts a degree of freedomof design.

[0011]FIG. 10 shows a relationship among a secondary light sourcedistribution, a pupil transmittance distribution, and an effective lightsource distribution in an exposure apparatus having a high NA. Thesecondary light source distribution is set to have a uniform coherencefactor a σ=0.8, similar to FIG. 9. However, the lower pupiltransmittance distribution at its peripheral as shown in the middle inFIG. 10 results in a non-uniform effective light source distribution, aswell as a non-uniform effective σ value of less of less than 0.8.

[0012]FIG. 11 shows a relationship among a secondary light sourcedistribution, a pupil transmittance distribution, and an effective lightsource distribution in an exposure apparatus having a catadioptricprojection optical system. The secondary light source distribution isset to have a uniform coherence factor σ=0.8, similar to FIG. 9.However, the non-uniform pupil transmittance distribution as shown inthe middle in FIG. 11 prevents from the effective light sourcedistribution from being uniform, as well as providing a non-uniformeffective σ value of less of less than 0.8. In particular, a mirror hasdifferent reflectance depending upon a deflection angle. Here, the pupiltransmittance in this application means optical use efficiency in anoptical system including reflectance.

[0013] Thus, the optical system in the exposure apparatus has differenttransmittances between part near the optical axis and part apart fromthe optical axis, and provides eccentric angular distribution of theexposure light incident onto the wafer (i.e., effective light sourcedistribution). Disadvantageously, this results in an undesirable angulardistribution of the exposure light incident onto the wafer surface(i.e., effective light source distribution) even when the secondarylight source distribution is adjusted to a desired distribution sincethe subsequent optical system has a non-uniform transmittancedistribution (or pupil transmittance distribution). In other words, apredetermined resolution critical dimension (in particular, minimum linewidth) cannot disadvantageously obtained because this results inexposure with a coherence factor different from a most suitable one.

[0014] This problem occurs at wafer center positions (on-axis) and waferperipheral (off-axis), but another problem of an offset center ofgravity occurs at the off-axis in which a deviation of an effectivelight source distribution incident onto the on-axis deviates differentlyfrom that incident onto the off-axis. As a result, in addition to theabove problem, the off-axis critical dimension to be transferred to thewafer is different according to positions.

BRIEF SUMMARY OF THE INVENTION

[0015] Accordingly, it is an exemplary object of the present inventionto provide an exposure method and apparatus, and device fabricationmethod, which may obtain improved angular distribution of exposure light(or effective light source distribution) even for non-uniformtransmittance distribution of an optical system (or pupil transmittancedistribution), and reduce a difference in effective light sourcedistribution between a substrate center and a substrate peripheral.

[0016] An exposure apparatus of one aspect of the present inventionincludes a projection optical system for exposing and transferring apattern on a mask onto an object, an illumination optical system forforming a secondary light source surface approximately conjugate with apupil in the projection optical system, and for illuminating the mask,and a mechanism for making non-uniform at least one of a transmittancedistribution from the secondary light source surface to the object and alight intensity distribution on the secondary light source surface.

[0017] The transmittance distribution and the light intensitydistribution on the secondary light source surface may be complementaryto each other. The light intensity distribution on the secondary lightsource surface may increase in a direction going away from the opticalaxis. The illumination optical system may include a first fly-eye lensfor illuminating the pattern on the mask, and a second fly-eye lens forilluminating the first fly-eye lens, wherein the mechanism includes acontroller for controlling transmittance according to an angulardistribution of exposure light near an exit end of the second fly-eyelens. The controller may increase the transmittance as an obliqueincidence angle of the exposure light increases. The controller mayinclude a glass plate onto which a film for controlling transmittance isapplied, the glass plate being inclinable relative to an optical axis.The controller may include plural members that have differenttransmittance control amounts and are exchangeable according toillumination conditions.

[0018] An exposure apparatus of another aspect of the present inventionincludes a projection optical system for exposing and transferring apattern on a mask onto an object, an illumination optical system forforming a secondary light source surface approximately conjugate with apupil in the projection optical system, and for illuminating the mask,and a secondary light-source adjusting mechanism for adjusting a lightintensity distribution on the secondary light source surface accordingto transmittance distributions from the secondary light source surfaceto the object.

[0019] The secondary light-source adjusting mechanism may adjust thelight intensity distribution on the secondary light source surfaceaccording to the transmittance distributions from the secondary lightsource surface to the object and switching illumination conditions. Thesecondary light-source adjusting mechanism may adjust an angulardistribution of exposure light incident onto the object. The secondarylight-source adjusting mechanism may adjust the light intensitydistribution on the secondary light source surface with respect to eachof a rotationally symmetrical component and a rotationally asymmetricalcomponent according to the transmittance distributions.

[0020] The secondary light-source adjusting mechanism may include acondenser optical system, a light mixture mechanism for reflecting andmixing light exiting from the condenser optical system, and an imagingzoom lens for imaging a light intensity distribution formed at an exitsurface of the light mixture mechanism at a position approximatelyconjugate with the secondary light source surface, wherein the secondarylight-source adjusting mechanism adjusts the light intensitydistribution on the secondary light source surface by adjusting adivergent angle from the condenser optical system. The exposureapparatus may further include a mechanism for adjusting a focal distanceof the condenser optical system according to the transmittancedistributions from the secondary light source surface to the object. Themechanism for adjusting the focal distance may adjust the focal distanceof the condenser optical system according to switching illuminationconditions. The exposure apparatus may further include a drive mechanismfor eccentrically driving divergent light emitted from the condenseroptical system relative to the light mixture mechanism. The drivemechanism may adjust an eccentricity amount according to switchingillumination conditions.

[0021] The secondary light-source adjusting mechanism may include acondenser optical system, a light mixture mechanism for reflecting andmixing light exiting from the condenser optical system, an imaging zoomlens for imaging a light intensity distribution formed at an exitsurface of the light mixture mechanism at a position approximatelyconjugate with the secondary light source surface, and a transmittancecorrection filter for correcting transmittance near an exit surface ofthe light mixture means. There may be plural transmittance correctionfilters for correcting the transmittance distribution with differentcorrection amounts in a rotationally symmetrical manner, and one of thefilters being exchangeably selected according to illuminationconditions. The exposure apparatus may further include a drive mechanismfor driving and shifting the transmittance correction filter in aparallel direction with a shift amount that is adjustable according toswitching illumination conditions.

[0022] The secondary light-source adjusting mechanism may include acondenser optical system, a light mixture mechanism for reflecting andmixing light exiting from the condenser optical system, and an imagingzoom lens for imaging a light intensity distribution formed at an exitsurface of the light mixture mechanism at a position approximatelyconjugate with the secondary light source surface, wherein the imagingzoom lens serves to adjust distortion according to transmittancedistributions from the secondary light source surface to the object. Theexposure apparatus may further include a detector for detecting anangular distribution of exposure light incident onto the object, and thesecondary light-source adjusting mechanism drives according to adetection result by the detector.

[0023] An exposure apparatus of another aspect of the present inventionincludes a projection optical system for exposing and transferring apattern on a mask onto an object, an illumination optical system forforming a secondary light source approximately conjugate with a pupil inthe projection optical system, and for illuminating the mask, and aconvex meniscus lens provided at the object or at a positionapproximately conjugate with the object according to transmittancedistributions from the secondary light source surface to the object.

[0024] The above exposure apparatus may expose the pattern on the maskonto the object through the projection optical system by sequentiallymoving the mask and the object to positions corresponding to aprojection demagnification of the projection optical system in adirection perpendicular to an optical axis in the projection opticalsystem. Alternatively, the above exposure apparatus may expose thepattern on the mask onto the object through the projection opticalsystem by moving the mask and the object to positions at a speed ratiocorresponding to a projection demagnification of the projection opticalsystem in a direction perpendicular to an optical axis in the projectionoptical system.

[0025] An exposure method of another aspect of the present invention forprojecting and exposing a pattern on a mask onto an object using theabove exposure apparatus includes the steps of detecting a change of anangular distribution of exposure light incident on the object, andcorrecting the angular distribution based on a detection result.

[0026] A device fabricating method includes the steps of projecting andexposing a pattern on a mask onto an object using the above exposureapparatus, and developing the exposed object.

[0027] Claims for the device fabricating method that exhibits operationssimilar to those of the above exposure apparatus cover devices as theirintermediate products and finished products. Moreover, such devicesinclude, e.g., semiconductor chips such as LSIs and VLSIs, CCDs, LCDs,magnetic sensors, thin-film magnetic heads, etc.

[0028] Other objects and further features of the present invention willbecome readily apparent from the following description of theembodiments with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a schematic view of a simplified optical path in anexposure apparatus of a first embodiment according to the presentinvention.

[0030]FIG. 2 is a graph for showing an illumination distribution in anoptical pipe or secondary light source surface.

[0031]FIG. 3 is a schematic view of a simplified optical path in anexposure apparatus of a second embodiment according to the presentinvention.

[0032]FIG. 4 is a schematic sectional view for explaining a method forcorrecting a difference between pupil transmittance of an on-axis andthat of an off-axis.

[0033]FIG. 5 is a flowchart showing a correction of effective lightsource distribution of one embodiment.

[0034]FIG. 6 is a sectional view showing a measuring method of anexposure-light angular distribution of one embodiment.

[0035]FIG. 7 is a flowchart for explaining a fabrication of devices(semiconductor chips such as ICs, LSIs, and the like, LCDs, CCDs, etc.).

[0036]FIG. 8 is a detailed flowchart for Step 4 Wafer shown in FIG. 7.

[0037]FIG. 9 shows a relationship among a secondary light sourcedistribution, a pupil transmittance distribution, and an effective lightsource distribution in a conventional exposure apparatus.

[0038]FIG. 10 shows a relationship among a secondary light sourcedistribution, a pupil transmittance distribution, and an effective lightsource distribution in a conventional exposure apparatus using a higherNA and a shorter wavelength of light.

[0039]FIG. 11 shows a relationship among a secondary light sourcedistribution, a pupil transmittance distribution, and an effective lightsource distribution in a conventional exposure apparatus using acatadioptric projection optical system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] A description will now be given of an exposure apparatus 100 of afirst embodiment according to the present invention with reference tothe accompanying drawings. Here, FIG. 1 is a schematic view of asimplified optical path in the exposure apparatus 100. The exposureapparatus 100 includes an illumination apparatus, a reticle 13, aprojection optical system 14, and a plate 15. The exposure apparatus 100is a projection exposure apparatus for exposing a circuit pattern formedon the reticle 13 onto the plate 15 in a step-and-repeat method andstep-and-scan method.

[0041] The illumination apparatus illuminates the reticle 13 that formsa circuit pattern to be transferred, and includes a light source partand an illumination optical system.

[0042] The light source part includes a light source 1 and a beamshaping system 2.

[0043] The light source 1 may use, for example, an ArF excimer laserwith a wavelength of about 193 nm, an F₂ excimer laser of a wavelengthof about 157 nm, etc. The beam shaping system 2 may use, for example, abeam expander having a plurality of cylindrical lenses etc., and convertparallel light having a different aspect ratio from the laser lightsource 1 into a desired value (for example, by changing the sectionalshape from a rectangle to a square), thus shaping the beam shape to adesired one. The beam shaping system 2 forms a beam that has a size anda divergent angle needed to illuminate the fly-eye lens 6, which will bedescribed later.

[0044] The illumination optical system illuminates the mask 13, andincludes a condenser optical system 3, an optical pipe 4 as a beammixture means, an imaging zoom lens 5, a fly-eye lens 6, a stop 7, anilluminating lens 8, a field stop 9, imaging lenses 10 and 11, and adeflection mirror 12. The condenser optical system 3 condenses light,which has passed through the beam shaping system 2, near an incidentsurface 4 a of the optical pipe 4, providing light entering the opticalpipe 4 with a predetermined divergent angle. The condenser opticalsystem 3 includes at least one lens element and a necessary deflectingmirror for deflecting the optical path. When the optical pipe 4 is madeof a glass rod, a condensing point P by the condenser optical system 3is defocused toward the light source from the incident surface 4 a ofthe optical pipe 4, in order to enhance a coating (or reflectionprevention film) at a glass-rod incident surface or endurance of theglass material itself.

[0045] The optical pipe 4 makes uniform, at its exit surface, the lightintensity distribution that is not uniform at its incident surface as aresult of repetitive side reflections of light entering from thecondensing point P at a specific divergent angle.

[0046] The optical pipe 4 in this embodiment forms reflection surfacesof a hexagonal sectional shape, and is made, for example, of aglass-molded hexagonal column rod. Of course, such a structure isexemplary, and the section may be m-gonal (m: even number) or circularor a hollow rod.

[0047] The imaging zoom lens 5 images the optical pipe 4's exit surface4 b onto the fly-eye lens 6's incident surface under a specificdemagnification, and both are in an approximately conjugaterelationship. The zoom lens with a variable demagnification may adjust arange of light incident upon the fly-eye lens 6, and form multipleillumination conditions (or coherence factor σ values, i.e.,illumination optical system's NA/projection optical system's NA).

[0048] The fly-eye lens 6 serves to provide a uniform illumination to anobject plane. The fly-eye lens 6 is a wavefront splitting type opticalintegrator for splitting a wavefront of incident light, and for creatingmultiple light sources at or near an exit surface. The fly-eye lens 6converts an angular distribution of incident light into a positionaldistribution. The incident surface and the exit surface on the fly-eyelens 6 are in a Fourier transformation relationship (the Fouriertransformation relationship in the present specification means anoptical relationship of a pupil plane and an object plane (or an imageplane), and an object plane (an image plane) and a pupil plane.) Thus,the neighborhood of the fly-eye lens 6′ exit surface 6 b is a secondarylight source. The fly-eye lens 6 is structured by combining many rodlenses (namely, fine lens elements) in this embodiment. However, thewavefront splitting type optical integrator applicable to the instantinvention is not limited to a fly-eye lens, and it can be, for example,multiple sets of cylindrical lens array plates in which respective setsare arranged orthogonal to each other.

[0049] The stop 7 is a variable aperture stop that shields unnecessarylight, creates a desired effective light source, and may use variousstops having an ordinary circle, an annular illumination, etc. In orderto replace a variable aperture stop, a disc turret that forms suchaperture stops 7 may be prepared and a controller and drive mechanism(not shown) may switch the aperture by turning the turret, for instance.

[0050] The illumination lens 8 is, for example, a condenser lens forcondensing as many secondary light sources formed near the fly-eye lens6's exit surface 6 b as possible, for superimposing them on the fieldstop 9, and for Koehler-illuminating the field stop 9.

[0051] The field stop 9 includes multiple mobile light blocking platesfor forming an arbitrary aperture shape, and limits an exposure range onthe reticle 13 surface as a surface to be illuminated (and even thewafer 15).

[0052]10 and 11 are imaging lenses for transferring an aperture shape ofthe field stop 9 onto the reticle 13 as a plane to be illuminated. 12 isa deflecting mirror that deflects light emitted from the imaging lens 10so that it may enter the imaging lens 11 (and thus the mask 13). Whenthe imaging lens 210 is arranged parallel to the imaging lens 10 inadvance, the deflecting mirror 12 may be omitted. However, thedeflecting mirror 12 in this structure contributes to miniaturization ofthe apparatus.

[0053] The mask 13 is, e.g., of quartz, on which a circuit pattern (oran image) to be transferred is created, and is supported and driven by amask stage (not shown). Diffracted light through the mask 13 isprojected through the projection optical system 14 onto the plate orwafer 15. The plate 15 is a target to be exposed, onto which resist isapplied. The mask 13 and the plate 15 are located in a conjugaterelationship. When the exposure apparatus 100 is a step-and-scan typeexposure apparatus (namely, a scanner), it scans the mask 13 and theplate 15 to transfer the pattern on the mask 13 onto the plate 15. Whenthe exposure apparatus 100 is a step-and-repeat type exposure apparatus(i.e., “a stepper”), the mask 13 and the plate 15 are kept stationaryfor exposure.

[0054] The mask stage (not shown) supports the mask 13, and is connectedto a transport mechanism (not shown). The mask stage and projectionoptical system 14 are installed on a stage lens barrel stool supportedvia a damper, for example, to the base-frame placed on the floor. Themask stage may use any structure known in the art. The transportmechanism (not shown) is made up of a linear motor and the like, anddrives the mask stage in a direction orthogonal to the optical axis,thus moving the mask 13. The exposure apparatus 100 uses a control unit(not shown) to synchronously scan the mask 13 and the plate 15.

[0055] The projection optical system 14 images, onto the plate 15, lightthat has passed through the pattern formed on the mask 13. Theprojection optical system 14 may use an optical system solely composedof a plurality of lens elements, an optical system comprised of aplurality of lens elements and at least one concave mirror (acatadioptric optical system), an optical system comprised of a pluralityof lens elements and at least one diffractive optical element such as akinoform, and a full mirror type optical system, and so on. Anynecessary correction of the chromatic aberration may use a plurality oflens units made from glass materials having different dispersion values(Abbe values), or arrange a diffractive optical element such that itdisperses in a direction opposite to that of the lens unit.

[0056] The plate 15 is a wafer in this embodiment, but it may include aliquid crystal plate and a wide range of other objects to be exposed.Photoresist is applied onto the plate 15. A photoresist application stepincludes a pretreatment, an adhesion accelerator application treatment,a photoresist application treatment, and a pre-bake treatment. Thepretreatment includes cleaning, drying, etc. The adhesion acceleratorapplication treatment is a surface reforming process so as to enhancethe adhesion between the photoresist and a base (i.e., a process toincrease the hydrophobicity by applying a surface active agent); througha coat or vaporous process using an organic film such as HMDS(Hexamethyl-disilazane). The pre-bake treatment is a baking (or burning)step, softer than that after development, which removes the solvent.

[0057] The plate 15 is supported by a wafer stage (not shown). The waferstage may use any structure known in the art, and a detailed descriptionof its structure and operations will be omitted. For example, the waferstage uses a linear motor to move the plate 15 in a direction orthogonalto the optical axis. The mask 13 and plate 15 are, for example, scannedsynchronously, and positions of the mask stage and wafer stage aremonitored, for example, by a laser interferometer and the like, so thatboth are driven at a constant speed ratio. The wafer stage is installedon a stage barrel surface supported on the floor and the like, forexample, via a damper.

[0058] The instant embodiment contemplates a situation where the pupiltransmittance distribution of the optical system from the secondarylight source surface to the plate 15, which will be described later,becomes as shown in the middle of FIG. 10 with the shorter wavelength ofthe exposure light and higher NA. Since the pupil transmittancedistribution in this situation tends to be lower at its peripheral, adesired effective light source distribution needs an adjustment thatenhances the secondary light source distribution at its peripheral. Adescription will now be given of the secondary light-source adjustingmechanism.

[0059] (First Adjusting Mechanism)

[0060] Since it has been known from the optical simulation that thelight intensity distribution at the optical pipe 4's exit end 4 bchanges as shown in FIG. 2 according to the number of reflections oflight that propagates in the optical pipe 4, the condenser opticalsystem 3 is made of a zoom optical system that has a variable focaldistance and the NA of light incident on the optical pipe 4 is madeadjustable so as to make variable the number of reflections of lightthat propagates in the optical pipe 4. An adjustment that enables thelight intensity distribution on the optical-pipe exit end 4 b toincrease at its peripheral would increase the light intensitydistribution on the secondary light source surface 6 b at itsperipheral.

[0061] Such an adjustment of the focal distance of the condenser opticalsystem 3 according to illumination conditions would provide the mosteffective light source distribution for each illumination condition.Alternatively, rather than making the condenser optical system 3 of thezoom optical system, it may be an optical system 3′ having a differentfocal distance according to a switch of an illumination condition.

[0062] (Second Adjusting Mechanism)

[0063] The focal distance of the condenser optical system 3 is fixedwhen the light intensity distribution on the optical-pipe exit end 4 bexhibits a certain state. An ND filter is provided near the optical-pipeexit end 4 b to adjust the light intensity distribution of the secondarylight source surface. The transmittance distribution of the ND filter isadjusted such that the peripheral transmittance is higher than thecenter transmittance. Plural ND filters 20 a to 20 d having differenttransmittances are prepared, and made selectable by a turret 20 for eachillumination condition.

[0064] (Third Adjusting Mechanism)

[0065] The focal distance of the condenser optical system 3 is fixedwhen the light intensity distribution on the optical-pipe exit end 4bexhibits a certain state. The light intensity distribution on thesecondary light source surface 6 b is made adjustable as shown in FIG.2, by making the imaging zoom lens 5 of a zoom lens having variabledistortion.

[0066] At least one of the above first to third adjusting mechanismscould adjust the secondary light source distribution for a desiredeffective light source distribution according to pupil transmittancedistributions after the secondary light source surface 6 b.

[0067] They are particularly effective to the pupil transmittancedistribution that has a rotational symmetry and a decreased peripheral.

[0068]FIG. 3 is a schematic view of a simplified optical path of theexposure apparatus 100 a of a second embodiment according to the presentinvention. It is different from the exposure apparatus 100 in that ithas a projection optical system of a catadioptric system. Those elementsin FIG. 3 which are corresponding elements in FIG. 1 are designated bythe same reference numerals.

[0069] The instant embodiment contemplates that the pupil transmittancedistribution in the optical system from the secondary light sourcesurface 6 b to the wafer 15 has an inclination shown in the middle ofFIG. 11. A detailed description will now be given of the secondary lightsource adjusting mechanism for obtaining a desired effective lightsource distribution for this pupil transmittance distribution.

[0070] (Fourth Adjusting Mechanism)

[0071] An effect of changing the focal distance of the condenser opticalsystem 3 has been discussed for the first adjusting mechanism. Theinstant adjustment is characterized in that the distribution on the exitend 4 b is inclined in a direction to cancel out the pupil transmittancedistribution by biasing the light distribution incident onto the opticalpipe 4.

[0072] This may be implemented, for example, by inclining the condenseroptical system 3 eccentrically, or by decentering the condenser opticalsystem 3 in parallel. Preferably, a function is provided for adjustingan eccentric amount according to switching illumination conditions.

[0073] Thus, the light intensity distribution of the secondary lightsource surface may be properly adjusted by making the condenser opticalsystem 3 of a zoom optical system having a variable focal distance, andby decentering the optical element before the optical pipe 4. Thecondenser optical system 3 may include plural members that havedifferent focal distances and are replaceable according to switchingillumination conditions.

[0074] (Fifth Adjusting Mechanism)

[0075] The focal distance of the condenser optical system 3 is fixedwhen the light intensity distribution on the optical-pipe exit end 4 bexhibits a certain state. An ND filter 20 is provided near theoptical-pipe exit end 4 b. The effect of this arrangement has beendiscussed for the second adjusting mechanism. The instant adjustmentinclines the distribution on the secondary light source distribution ina direction to cancel out the pupil transmittance distribution byparallel shifting the ND filter 20.

[0076] Therefore, the ND filter is mounted on a drive mechanism foradjusting a shift amount, and the drive mechanism adjusts to the bestshift amount for each illumination condition. Plural ND filters 20 a to20 d having different transmittances are prepared, and made selectableaccording to switching illumination conditions.

[0077] At least one of the above first to fifth adjusting mechanismscould adjust the secondary light source distribution for a desiredeffective light source distribution according to pupil transmittancedistributions after the secondary light source surface 6 b.

[0078] They are particularly effective to the pupil transmittancedistribution that mixes a rotationally symmetric component and arotationally asymmetric component.

[0079] The optical system shown in FIG. 1 is exemplary, and a secondfly-eye lens may be, for example, used instead of the optical pipe 4.

[0080] This case additionally uses a condenser lens instead of theimaging zoom lens 5 for superimposing and Koehler-illuminating lightfrom the newly introduced second fly-eye lens on the subsequent fly-eyelens 6.

[0081] The adjusting mechanism is provided near the exit surface of thesecond fly-eye lens controls the transmittance in accordance with theangular distribution of the exposure light.

[0082] For example, a plate is inclinably arranged onto which atransmission control film that has characteristics of the transmittanceof 93% at an incident angle of 0° and the transmittance of 98% at anincident angle of 5°. Plural plates having different transmissioncontrol amounts are prepared and replaceable according to switchingillumination conditions. The inclination amount is also made variable.

[0083] Next follows a description of an adjusting mechanism forbalancing the effective light source distributions at the center of andperipheral of the substrate. In general, the transmission loss of lightthat has passed many optical elements increases when the light hastransmitted through part farther from the optical axis. Therefore, thepupil transmittance distribution of light that reaches the substrateperipheral (or off-axis) is likely to provide a rotationallyasymmetrical distribution that inclines from the substrate center (oron-axis).

[0084] Although it is desirable to use the above first and fifthadjusting mechanisms to adjust and balance the on-axis and off-axiseffective light source distributions in a permissible range, thisrequires a correction mechanism for correcting a difference betweenon-axis and off-axis pupil transmittance distributions to some extent.

[0085] A detailed description will now be given of the correctionmechanism with, reference to FIG. 4. The off-axis beams incident ontothe plate 15 include a beam 30 closer to the optical axis and a beam 31farther to the optical axis. The beam 31 receives a larger transmissionloss than the beam 30 after transmitting through optical elements to theplate 15, and provides an off-axis effective light source distributionof a rotational asymmetry near the substrate peripheral.

[0086] In order to reduce a light-amount difference between the off-axisbeam 30 and beam 31, a lens 33 is preferably a convex meniscus lens nearthe plate 15 or the reticle 13 or field stop 9 conjugate with the plate15.

[0087] The beam 30 incident onto the convex meniscus lens 33 has a largeangle with a large transmission loss, whereas the light 31 has a smallangle with a small transmission loss. Thus, an effect of a reducedlight-amount difference may be expected between the beams 30 and 31 thatreach the wafer 15, with the off-axis excellent pupil transmittancedistribution.

[0088]FIG. 5 is a flowchart for explaining a method for adjusting thesecondary light source distribution. Step 101 calculates transmittancefor each illumination condition from a wafer center to a waferperipheral, referring to designed values (such as a lens design value,coating characteristic, glass material transmittance, and mirrorreflection), and obtains approximate pupil transmittance distribution.The default setup for the secondary light-source adjusting mechanism isset based on the calculated pupil transmittance distributioninformation. Step 103 measures the angular distribution or effectivelight source distribution after Step 102 switches an illumination mode.

[0089] There are conceivable various methods for measuring the angulardistribution of the exposure light, including, for example, a method fordriving the field stop 9 to set a fine aperture corresponding to thesubstrate position to be measured, and for defocusing a detector 40provided near the plate or wafer 15 in an optical-axis Z direction froman actual plate reference surface, while offsetting the reticle 13 outof the optical path. FIG. 6A shows the apparatus in this state. Thoseelements in FIG. 6A, which are the same as corresponding elements inFIG. 1 are designated by the same reference numerals. In addition, FIG.6A omits the deflection mirror 12 for simplified description.

[0090] Only the exposure light limited by the field stop 9 once imageson the plate 15 surface, and enters the detector 40 while reflecting itsangle. The detector 40 is provided on the XY stage 41 for holding theplate 15, and has a pinhole at the top of its light-receiving surfacewhich is small enough for the spread light. The XY stage horizontallymoves this detector 40, for example, in a two-dimensionally spreadingrange, measures the incident-light intensity, and determines the angulardistribution of the exposure light. A two-dimensional CCD may be usedinstead of the detector.

[0091] A similar measurement is available by providing a fine apertureat a position conjugate with the field stop 9. More specifically, it isconceivable as shown in FIG. 6B that the field stop 9 is released and adedicated reticle using a Cr pattern to form a fine aperture isprovided.

[0092] An angular distribution at each image point may be measuredthrough measurements at arbitrary points using the above method.

[0093] The measured and detected angular distribution information issent to a main controller (not shown), and Step 104 determines whetherit is a desired effective light source distribution. If it is not, Step105 instructs the main controller to calculate a drive amount and drivedirection of the secondary light source adjusting mechanism, and Step106 drives the secondary light source adjusting mechanism with apredetermined amount and direction. The procedure is fed back to Step103 after driving, and measures the angular distribution of the exposurelight again. When the effective light source distribution has apredetermined value, the adjustment ends. Otherwise, the aboveprocedures repeat until it becomes a proper value.

[0094] A description will now be given of an exposure operation of theexposure apparatus shown in FIG. 1. In exposure, a beam emitted from thelight source 1 is shaped into a desired beam shape by the beam shapingsystem 2, and then enters the condenser optical system 3. The laser beamfrom the condenser optical system 3 once condenses or images at thepoint P, and then enters as divergent light having a divergent angle theoptical pipe 4.

[0095] The imaging zoom lens 5 images the optical pipe 4's exit surface4 b on the fly-eye 6's incident surface 6 a with a predetermineddemagnification. The above adjusting mechanism adjusts the secondarylight source distribution formed near the fly-eye 6's exit surface 6 bbased on the subsequent transmittance distribution. The fly-eye lens 6transmits the stop 7, and illuminates the field stop 9 through theillumination lens 8. The light that has passed the field stop 9 passesthe imaging lens 10 and 11, and then illuminates the mask 13 surface.

[0096] The light, which has passed through the mask 13 is demagnifiedand projected under a specific demagnification onto the plate 15 throughthe imaging operation of the projection optical system 14. The angulardistribution or effective light source distribution on the plate 15becomes almost uniform due to the adjusting mechanism. When the exposureapparatus 100 is a stepper, the light source part and the projectionoptical system 14 are fixed, the mask 13 and plate 15 are synchronouslyscanned for exposure to all the shots. The wafer stage for the plate 15is stepped to the next shot so as to expose and transfer a large numberof shots onto the plate 15. On the other hand, the exposure apparatus100 as a scanner would provide exposure with the mask 13 and the plate15 in a stationary state.

[0097] Since the inventive exposure apparatus 199 uses the adjustingmechanism to make uniform the effective light source distribution bymaking complementary the secondary light source distribution andtransmittance distribution, performing a pattern transfer to the resistwith high precision, and providing high quality devices (such assemiconductor devices, LCD devices, image pick-up devices (such asCCDs), thin film magnetic heads, and the like).

[0098] A description will now be given of an embodiment of a devicefabricating method using the above mentioned exposure apparatus 100.FIG. 7 is a flowchart for explaining how to fabricate devices (i.e.,semiconductor chips such as IC and LSI, LCDs, CCDs, etc.). Here, adescription will be given of the fabrication of a semiconductor chip asan example. Step 1 (circuit design) designs a semiconductor devicecircuit. Step 2 (mask fabrication) forms a mask having a designedcircuit pattern. Step 3 (wafer making) manufactures a wafer usingmaterials such as silicon. Step 4 (wafer process), which is alsoreferred to as a pretreatment, forms actual circuitry on the waferthrough photolithography of the present invention using the mask andwafer. Step 5 (assembly), which is also referred to as a posttreatment,forms into a semiconductor chip the wafer formed in Step 4 and includesan assembly step (e.g., dicing, bonding), a packaging step (chipsealing), and the like. Step 6 (inspection) performs various tests forthe semiconductor device made in Step 5, such as a validity test and adurability test. Through these steps, a semiconductor device is finishedand shipped (Step 7).

[0099]FIG. 8 is a detailed flowchart of the wafer process in Step 4.Step 11 (oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms aninsulating film on the wafer's surface. Step 13 (electrode formation)forms electrodes on the wafer by vapor disposition and the like. Step 14(ion implantation) implants ion into the wafer. Step 15 (resist process)applies a photosensitive material onto the wafer. Step 16 (exposure)uses the exposure apparatus 1 to expose a circuit pattern on the maskonto the wafer. Step 17 a(development) develops the exposed wafer. Step18 (etching) etches parts other than a developed resist image. Step 19(resist stripping) removes disused resist after etching.

[0100] These steps are repeated, and multi-layer circuit patterns areformed on the wafer. The fabrication method of this embodiment wouldmanufacture high quality semiconductor devices faster than theconventional method.

[0101] According to the instant embodiment, a desired effective lightsource distribution or angular distribution of exposure light incidentonto a substrate may be obtained by adjusting the secondary light sourcedistribution according to the transmittance distribution from thesecondary light source surface to the substrate. A convex meniscus lensprovide near a surface conjugate with the substrate would reduce adifference between on-axis and off-axis effective light sourcedistributions. Thus, the exposure apparatus using a short wavelength anda high NA may form a desired effective light source distribution, andmaintain its transfer performance with high precision.

[0102] Thus, the inventive exposure apparatus and method, and devicefabrication method may obtain improved angular distribution of exposurelight (or effective light source distribution) even for non-uniformtransmittance distribution of an optical system (or pupil transmittancedistribution), and reduce a difference in effective light sourcedistribution between a substrate center and a substrate peripheral.

What is claimed is:
 1. An exposure apparatus comprising: a projectionoptical system for exposing and transferring a pattern on a mask onto anobject; an illumination optical system for forming a secondary lightsource surface approximately conjugate with a pupil in said projectionoptical system, and for illuminating the mask; and a mechanism formaking non-uniform at least one of a transmittance distribution from thesecondary light source surface to the object and a light intensitydistribution on the secondary light source surface.
 2. An exposureapparatus according to claim 1, wherein the transmittance distributionand the light intensity distribution on the secondary light sourcesurface are complementary to each other.
 3. An exposure apparatusaccording to claim 1, wherein the light intensity distribution on thesecondary light source surface increases in a direction going away fromthe optical axis.
 4. An exposure apparatus according to claim 1, whereinsaid illumination optical system includes: a first fly-eye lens forilluminating the pattern on the mask; and a second fly-eye lens forilluminating the first fly-eye lens, wherein said mechanism includes acontroller for controlling transmittance according to an incident angleof exposure light near an exit end of the second fly-eye lens.
 5. Anexposure apparatus according to claim 4, wherein said controllerincreases the transmittance as an oblique incidence angle of theexposure light increases.
 6. An exposure apparatus according to claim 4,wherein said controller includes a glass plate onto which a film forcontrolling transmittance is applied, the glass plate being inclinablerelative to an optical axis.
 7. An exposure apparatus according to claim4, wherein said controller includes plural members that have differenttransmittance control amounts and are exchangeable according toillumination conditions.
 8. An exposure apparatus comprising: aprojection optical system for exposing and transferring a pattern on amask onto an object; an illumination optical system for forming asecondary light source surface approximately conjugate with a pupil insaid projection optical system, and for illuminating the mask; and asecondary light-source adjusting mechanism for adjusting a lightintensity distribution on the secondary light source surface accordingto transmittance distributions from the secondary light source surfaceto the object.
 9. An exposure apparatus according to claim 8, whereinsaid secondary light-source adjusting mechanism adjusts the lightintensity distribution on the secondary light source surface accordingto the transmittance distributions from the secondary light sourcesurface to the object and switching illumination conditions.
 10. Anexposure apparatus according to claim 8, wherein said secondarylight-source adjusting mechanism adjusts an angular distribution ofexposure light incident onto the object.
 11. An exposure apparatusaccording to claim 8, wherein said secondary light-source adjustingmechanism adjusts the light intensity distribution on the secondarylight source surface with respect to each of a rotationally symmetricalcomponent and a rotationally asymmetrical component according to thetransmittance distributions.
 12. An exposure apparatus according toclaim 8, wherein said secondary light-source adjusting mechanismincludes: a condenser optical system; a light mixture mechanism forreflecting and mixing light exiting from said condenser optical system;and an imaging zoom lens for imaging a light intensity distributionformed at an exit surface of said light mixture mechanism at a positionapproximately conjugate with the secondary light source surface, whereinsaid secondary light-source adjusting mechanism adjusts the lightintensity distribution on the secondary light source surface byadjusting a divergent angle from said condenser optical system.
 13. Anexposure apparatus according to claim 12, further comprising a mechanismfor adjusting a focal distance of said condenser optical systemaccording to the transmittance distributions from the secondary lightsource surface to the object.
 14. An exposure apparatus according toclaim 13, wherein said mechanism for adjusting the focal distanceadjusts the focal distance of said condenser optical system according toswitching illumination conditions.
 15. An exposure apparatus accordingto claim 12, further comprising a drive mechanism for eccentricallydriving divergent light emitted from said condenser optical systemrelative to said light mixture mechanism.
 16. An exposure apparatusaccording to claim 15, wherein said drive mechanism adjusts aneccentricity amount according to switching illumination conditions. 17.An exposure apparatus according to claim 8, wherein said secondarylight-source adjusting mechanism includes: a condenser optical system; alight mixture mechanism for reflecting and mixing light exiting fromsaid condenser optical system; an imaging zoom lens for imaging a lightintensity distribution formed at an exit surface of said light mixturemechanism at a position approximately conjugate with the secondary lightsource surface; and a transmittance correction filter for correctingtransmittance near an exit surface of said light mixture means.
 18. Anexposure apparatus according to claim 17, wherein there are pluraltransmittance correction filters for correcting the transmittancedistribution with different correction amounts in a rotationallysymmetrical manner, and one of the filters being exchangeably selectedaccording to illumination conditions.
 19. An exposure apparatusaccording to claim 17, further comprising a drive mechanism for drivingand shifting the transmittance correction filter in a parallel directionwith a shift amount that is adjustable according to switchingillumination conditions.
 20. An exposure apparatus according to claim 8,wherein said secondary light-source adjusting mechanism includes: acondenser optical system; a light mixture mechanism for reflecting andmixing light exiting from said condenser optical system; and an imagingzoom lens for imaging a light intensity distribution formed at an exitsurface of said light mixture mechanism at a position approximatelyconjugate with the secondary light source surface, wherein said imagingzoom lens serves to adjust distortion according to transmittancedistributions from the secondary light source surface to the object. 21.An exposure apparatus according to claim 8, further comprising adetector for detecting an angular distribution of exposure lightincident onto the object, and said secondary light-source adjustingmechanism drives according to a detection result by said detector. 22.An exposure apparatus comprising: a projection optical system forexposing and transferring a pattern on a mask onto an object; anillumination optical system for forming a secondary light sourceapproximately conjugate with a pupil in said projection optical system,and for illuminating the mask; and a convex meniscus lens provided atthe object or at a position approximately conjugate with the objectaccording to transmittance distributions from the secondary light sourcesurface to the object.
 23. An exposure apparatus according to claim 1,wherein said exposure apparatus exposes the pattern on the mask onto theobject through said projection optical system by sequentially moving themask and the object to positions corresponding to a projectiondemagnification of said projection optical system in a directionperpendicular to an optical axis in said projection optical system. 24.An exposure apparatus according to claim 1, wherein said exposureapparatus exposes the pattern on the mask onto the object through saidprojection optical system by moving the mask and the object to positionsat a speed ratio corresponding to a projection demagnification of saidprojection optical system in a direction perpendicular to an opticalaxis in said projection optical system.
 25. An exposure method forprojecting and exposing a pattern on a mask onto an object using anexposure apparatus, said exposure method comprising the steps of:detecting a change of an angular distribution of exposure light incidenton the object; and correcting the angular distribution based on adetection result, wherein said exposure apparatus includes: a projectionoptical system for exposing and transferring a pattern on the mask ontothe object; an illumination optical system for forming a secondary lightsource surface approximately conjugate with a pupil in said projectionoptical system, and for illuminating the mask; and a secondarylight-source adjusting mechanism for adjusting a light intensitydistribution on the secondary light source surface according totransmittance distributions from the secondary light source surface tothe object.
 26. A device fabricating method comprising the steps of:projecting and exposing a pattern on a mask onto an object using anexposure apparatus; and developing the exposed object, wherein saidexposure apparatus includes: a projection optical system for exposingand transferring a pattern on a mask onto an object; an illuminationoptical system for forming a secondary light source approximatelyconjugate with a pupil in said projection optical system, and forilluminating the mask; and a mechanism for making non-uniform at leastone of a transmittance distribution from the secondary light sourcesurface to the object and a light intensity distribution on thesecondary light source surface.